The behavior may have evolved because tree trunks are a far better place for a tree-dwelling spider than the forest floor, an unfamiliar territory crawling with creatures looking for a meal, he says.

Free Falling

Yanoviak and his colleagues have spent years hunting for insects that can glide with precision. The researchers use a simple test: They drop creatures from a great height.

Their "drop tests" have shown that many ant species can "hang glide," making controlled aerial descents, as do immature praying mantises and grasshoppers. The first spiders the team tried, however, flunked.

The scientists finally auditioned large arachnids known as “flatties,” some of which live in the American tropics. Though flatties can be as big across as a soup can lid, they're not much thicker than a nickel—some even thinner. (Watch a video of the world's largest spider.)

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"Flattie" spiders are more agile than cats in their airborne maneuvers.

Photograph by Stephen P. Yanovik

Flatties are also fast, and many are so perfectly camouflaged that it’s almost impossible to see them unless they move.

To capture flatties for the new experiments, Yanoviak and his team climbed trees in the Panamanian jungle, where they climbed trees and popped plastic bags over any spiders that betrayed themselves by scuttling away.

The scientists gathered more flatties in the Peruvian rain forest, where walkwayshigh in the tree canopy made spider collection relatively easy.

Catlike Maneuvers

The team then dusted their research subjects with fluorescent powder to easily identify them and to keep the spiders from clinging to the insides of their receptacles.

Then, in the forests of both countries, the scientists dropped the spiders from a height of 65 to 80 feet (20 to 25 meters) above the ground.

The best skydivers could swerve to a landing after falling only 13 feet (4 meters) or so.

In the video footage, “you’ll see the spider steering as it goes through the tree,” Yanoviak says. “If it wants to turn left, it changes the angle of the right front leg. And if it wants to turn right, it does the same with the left front leg.”

However, it's uncertain whether the leg movements are actually steering the airborne spiders, Yanoviak cautioned. But their flatness probably helps them glide, he says.

Awesome Aerials

The flatties’ glide also impresses other scientists not involved in the new research.

Sarah Crews, an independent evolutionary biologist who’s an expert on flatties, says she’s “convinced” by the findings, which show spiders are just as capable of gliding as insects—but do the job differently. (Also see “How Do Spiders Walk Upside Down? Mystery Solved.”)

“These results are indeed surprising for a spider,” says Marie Herberstein, a behavioral ecologist at Australia’s Macquarie University and editor of the book Spider Behavior. “Spiders generally rely on dragline silk … as a safety line should they fall,” she says.

Adds study leader Yanoviak, “It’s awesome to see them do it. They’re so good at it.”